In applications such as accelerator magnets, fine filament superconductors are needed in order to minimize distortion caused in the magnetic field by magnetization. The magnetization is dependent on the critical current density, the ratio of the matrix to the superconductor and the diameter of the superconductor filament. Generally the ratio of the matrix to the superconductor is determined as a certain constant value, which is derived from the stability of the wire. In order to cut the production costs of the wire, the tendency is to minimize the amount of the expensive superconductor material. Therefore the critical current density must be as high as possible, but simultaneously--owing to magnetization--the diameter of the superconductor filament must be as small as possible. However, a short diameter of the filament means that the number of the super-conductor filaments must be increased in order to maintain the properties of the superconductor. Usually such superconductors are produced by multi-step extrusion, in which case the final product contains heterogeneous filament areas resulting from the intermediate extrusion steps. In a two-step or three-step extrusion method, there are created several local irregularities in the matrix to superconductor ratio. Moreover, each extrusion step is expensive, and the separate extrusion steps weaken the properties of the superconductor as well as increase the waste of the material.
In order to reduce the extrusion steps, there are developed superconductor packing methods, where a superconductor billet containing several thousands of superconductor rods can be compiled so that the extrusion of the superconductor billet is carried out in a one-step extrusion. In the publications Kreilick T. S., Gregory E., Wong J: The design and fabrication of strand for SSC magnet applications, ICEC 11, Berlin 1986, and Geometric considerations in the design and fabrication of multifilamentary superconducting composites, IEEE Transactions on magnetics, Vol. MAG-23, No 2, 1987, there is described a method where round superconductor rods are packed directly into a copper can. In the publication Kanithi H. C., Valaris P., Zeitlin B. A: A novel approach to make fine filament superconductor, Supercollider 4, Edited by Nonte J., 1992, the superconductor rods are packed in a copper tube. This same production of superconductor billets also is described in the U.S. Pat. No. 5,088,183, introducing a method for producing a superconductor made of a large amount of round monofilament rods. In this method, a multiple of round monofilament rods is compiled inside a thin-wall hexagonal tube, whereafter several similarly compiled hexagonal tubes are assembled inside the extrusion can, and the areas that remain open are packed with single rods. The said superconductor billet is further compacted, extruded and drawn to the desired wire size. In the packing methods described above, at least part of the rods remain without support, which as such makes it difficult to create an advantageous superconductor billet.